全文获取类型
收费全文 | 6460篇 |
免费 | 654篇 |
国内免费 | 39篇 |
专业分类
电工技术 | 14篇 |
综合类 | 239篇 |
化学工业 | 4916篇 |
金属工艺 | 46篇 |
机械仪表 | 24篇 |
建筑科学 | 98篇 |
矿业工程 | 19篇 |
能源动力 | 16篇 |
轻工业 | 403篇 |
水利工程 | 8篇 |
石油天然气 | 268篇 |
武器工业 | 4篇 |
无线电 | 202篇 |
一般工业技术 | 848篇 |
冶金工业 | 18篇 |
原子能技术 | 18篇 |
自动化技术 | 12篇 |
出版年
2024年 | 20篇 |
2023年 | 37篇 |
2022年 | 34篇 |
2021年 | 155篇 |
2020年 | 119篇 |
2019年 | 116篇 |
2018年 | 144篇 |
2017年 | 169篇 |
2016年 | 209篇 |
2015年 | 208篇 |
2014年 | 332篇 |
2013年 | 422篇 |
2012年 | 422篇 |
2011年 | 407篇 |
2010年 | 317篇 |
2009年 | 355篇 |
2008年 | 324篇 |
2007年 | 391篇 |
2006年 | 473篇 |
2005年 | 403篇 |
2004年 | 390篇 |
2003年 | 327篇 |
2002年 | 243篇 |
2001年 | 199篇 |
2000年 | 169篇 |
1999年 | 173篇 |
1998年 | 143篇 |
1997年 | 96篇 |
1996年 | 54篇 |
1995年 | 61篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 16篇 |
1989年 | 22篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 13篇 |
1982年 | 19篇 |
排序方式: 共有7153条查询结果,搜索用时 15 毫秒
61.
62.
乙酸乙烯酯(VAc)与丙烯酸(AA)在GeCl_4及BCl_3存在下通过自由基聚合可得到交替共聚物。对GeCl_4体系,聚合反应速率正比于[引发剂]~(0.5)。当VAc/AA=1:1(mol比)时有最大反应速率。CCl_4对本聚合反应无链转移作用。通过紫外光谱分析可证实VAc及AA均与GeC\(?)生成络合物;ESR分析表明,络合AA自由基较未络合AA有较强的阳离子特性,交替共聚的原因可能与络合AA自由基及活化单体络合物二者有关。 相似文献
63.
Development of structures in new cycloolefin copolymers (COCs) of ethylene–norbornene (E–NB) and ethylene–tetracyclododecene (E–TD) of different NB/TD compositions were investigated under uniaxial elongational flow. For E–NB copolymer, which has multiblock sequences, a shoulder in WAXD at 0.76 nm was evident besides its amorphous halo, and the relative intensity of the peak increased with increasing comonomer content (NB). The appearance of a new peak for E–TD copolymer, and a relatively higher intense peak for E–NB copolymer at the same position of 0.76 nm, indicated that local ordering of the segments occurred when the COC was subjected to uniaxial flow. A lower comonomer composition of elongated COC, at a constant Hencky strain rate, exhibited two Tg values, whereas a higher composition showed a single Tg. Both local ordering and segmentization occurred in low comonomer content COCs but only local ordering occurred in higher comonomer content COCs. Both the shear viscosity and roll processing experiments exhibited similar phenomena of segregation. A model is proposed to illustrate the structure of COC after uniaxial elongation/deformation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3421–3427, 2004 相似文献
64.
65.
The effects of oxyen plasma treatment on the surface chemistry of Spectra 1000® high modulus polyethylene fibers and on the mechanical properties of fiber-reinforced composites of the fibers in a Bis-GMA based acrylic resin have been studied. X-ray photoelectron spectroscopy and diffuse reflectance FTIR spectroscopy have been used to show that the majority of oxygen on the fiber surface exists mostly in the form of ether and/or epoxy linkages, with carbonyl-, carboxylic- and ester-containing compounds accounting for less than 10 percent of the total. While the untreated and plasma-treated fibers have similar chemical compositions, the surfaces of the plasma-treated fibers are more polar and the oxygen is chemically bonded instead of being merely physisorbed. The interfacial shear strength between the fibers and the acrylic resin is increased by a factor of 2.3 by the plasma treatment indicating the presence of a weak boundary layer on the surface of the untreated fibers. The hydrolytic stability of the composite interfaces was investigated for fibers sized with several Bis-GMA-based adhesives. Maximum stability was attained by sizing with Bis-GMA containing a peroxide catalyst or an amine accelerator. The flexural properties of composites utilizing plasma-treated and untreated fibers were compared in three-point bending. The ultimate bending loads for composites using treated fibers were much higher than those for composites with untreated fibers, but only a fraction of that for glass or Kevlar®-reinforced materials. 相似文献
66.
聚丙烯酸钾与腐植酸复合高吸水性树脂的合成研究 总被引:1,自引:0,他引:1
以腐植酸与丙烯酸聚合制备了高吸水性树脂,讨论了交联剂、引发剂以及KOH用量对聚丙烯酸与腐植酸高吸水性树脂吸水率的影响,结果显示在n(MBA)∶n(AA)=0.0005、n(KPS)∶n(AA)=0.0075、n(KOH)∶n(AA)约为0.70、温度为80℃的条件下合成时,其吸水倍率可达到最优值。而且在接近自然条件下(35℃)失水速度慢,保水时间可达100 h以上,重复吸水性能好。运用红外光谱分析了腐植酸与丙烯酸的反应机理。 相似文献
67.
68.
Thermal radical copolymerization of styrene (S) and maleimide (MI) at 125°C in diglyme in the presence of 2,2,6,6‐tetramethylpiperidin‐1‐yloxyl radical (TEMPO) was studied. Mole fractions of maleimide in the feed, FMI, varied in the range 0.1–0.9. A quasiliving reaction process proceeded yielding copolymers with a low polydispersity (Mw/Mn = 1.17–1.41). The found azeotropic composition, (FMI)A = 0.46, did not differ substantially from that (0.5) in the conventional radical S‐MI copolymerization. At a higher conversion or MI content in the feed, deactivation of the copolymer chains occurred. The obtained TEMPO‐terminated S‐MI copolymers readily initiated polymerization of styrene; chain extension of the macroinitiators took place, giving poly(S‐co‐MI)‐block‐poly(S) diblock copolymers. The synthesized copolymers containing S and MI units were characterized by elemental analysis, NMR spectroscopy, size‐exclusion chromatography, and differential scanning calorimetry. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1863–1868, 2004 相似文献
69.
Novel imide-aryl ether benzoxazole copolymers were prepared and their morphology and mechanical properties investigated. A key feature of these copolymers is the incorporation of a benzoxazole moiety by the use of 2,2′-bis[4-(3-aminophenoxy)phenyl]-6,6′-bibenzoxazole or 2,2′-bis[4-(4-aminophenoxy)-phenyl]-6,6′-bibenzoxazole as co-diamines in polyimide syntheses. The preparation of these diamines involved the nucleophilic aromatic substitution of 2,2′-bis(4-fluorophenyl)-6,6′-bibenzoxazole with either 3- or 4-aminophenol in the presence of K2CO3. The diamines were co-reacted with various compositions of pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) to synthesize the desired poly(amic acids). Films were cast and cured (350°C) to effect the imide formation, affording films with elongations between 40 and 110% and moduli in the 2000–2750 MPa range. The copolymers exhibited good dimensional (Tg in excess of 300°C) and thermal stability. Wide-angle X-ray diffraction measurements on the copolymers showed that the ordered morphology characteristic of PMDA/ODA polyimide was retained. Improvements in the auto-adhesion were observed, particularly in those copolymers which displayed a Tg. 相似文献
70.